Astronomy and Astrophysics – Astrophysics
Scientific paper
1998-02-06
Astronomy and Astrophysics
Astrophysics
15 pages, LaTeX, 11 figures, submitted to MNRAS
Scientific paper
10.1046/j.1365-8711.1998.01897.x
Using numerical techniques we studied the global stability of cooling flows in giant elliptical galaxies. As an initial equilibrium state we choose the hydrostatic gas recycling model (Kritsuk 1996). Non-equilibrium radiative cooling, stellar mass loss, heating by type Ia supernovae, distributed mass deposition, and thermal conductivity are included. Although the recycling model reproduces the basic X-ray observables, it appears to be unstable with respect to the development of inflow or outflow. In spherically symmetry the inflows are subject to a central cooling catastrophe, while the outflows saturate in a form of a subsonic galactic wind. Two-dimensional axisymmetric random velocity perturbations of the equilibrium model trigger the onset of a cooling catastrophe, which develops in an essentially non-spherical way. The simulations show a patchy pattern of mass deposition and the formation of hollow gas jets, which penetrate through the outflow down to the galaxy core. The X-ray observables of such a hybrid gas flow mimic those of the equilibrium recycling model, but the gas temperature exhibits a central depression. The mass deposition rate M_dot consists of two contributions of similar size: (i) a hydrostatic one resembling that of the equilibrium model, and (ii) a dynamical one which is related to the jets and is more concentrated to the centre. For a model galaxy, like NGC 4472, our 2D simulations predict M_dot = 2 M_sun/yr within the cooling radius for the advanced non-linear stage of the instability. We discuss the implications of these results to H_alpha nebulae and star formation in cooling flow galaxies and emphasize the need for high-resolution 3D simulations.
Boehringer Hans
Kritsuk Alexei
Mueller Ewald
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